The present invention relates to a process for the production of moldings or flat materials abased on foamed polyisocyanate polyadducts containing urethane groups and optionally urea groups by molding. Foamed materials of which the density is increased during thermoplastic molding are used as the polyisocyanate polyadducts. The invention also relates to the moldings thus obtained. The polyisocyanate polyadducts useful herein are thermoplastically moldable, but are not truly thermoplastic. In other words, the polyadducts soften under the heat and pressure conditions of the molding process to such an extent that they can be shaped without ever passing into the liquid state. True thermoplastics on the other hand are solid at room temperature and become liquid at higher temperatures.
It is known that moldings or flat materials can be produced by thermoplastically molding polyurethanes (cf. for example Becker/Braun, Kunststoffhandbuck, Vol. 7, "Polyurethane", Carl Hanser Verlag, Munchen/ Wien (1983), pages 428 et seq). The earliest known thermoplastic polyurethane elastomers were based on diisocyanates, relatively high molecular weight dihydroxy compounds (and more particularly relatively high molecular weight polyester diols) and low molecular weight diols as chain extenders. The polyurethanes had a linear structure, i.e. no crosslinkages or branches were in the molecule. The thermoplastic molding of polyurethanes having branched molecular structure is also known. Thus, German Offenlegungshriften 2,461,399, 2,164,381, 2,032,174 and 2,607,380, for example, describe the production and thermoplastic molding of polyurethane foams. German Offenlegungshrift 3,733,756 relates to the production of moldings or films based on polyisocyanate polyadducts having a density of at least 0.8 g/cm.sup.3. The polyisocyanate polyadducts are produced from i) isocyanate-reactive group containing compounds with molecular weights of from 1,800 to 1,200 and having a functionality in the context of the isocyanate addition reaction of at least 2.5 and ii) low molecular weight, preferably difunctional compounds containing isocyanate-reactive groups, and iii) isocyanates. According to the teaching of German Offenlegungshrift 3,733,756, the thermoplastically moldable polyisocyanate polyadducts may also contain fillers and reinforcing materials.